A block m1 strikes a stationary block m3 inelastically.  Another block m2 is kept on m3. Neglecting the friction between all contacting surfaces, the fractional decrease of K. E. of the system in collision is:

Since the impact between m1 and m3 is inelastic, m1 and m3 will move together towards right and m2 does not move due to the absence of friction.The velocity of the combined mass Hence, the correct choice is (3).